The present invention relates to an information recording/reproduction apparatus comprising a head movement control means and, more particularly, to an information recording/reproduction apparatus comprising a device for preventing overrunning of a head when head control is inappropriate.
In an information recording/reproduction apparatus such as an optical disk apparatus, laser beams are focused to form a 1-.mu.m beam spot using an objective lens, and information is recorded or reproduced using the small beam spot.
In order to increase an information retrieval speed, conventionally, an optical head is normally moved by a voice-coil type linear motor. In the apparatus of this type, upon retrieval of information, a current head position is detected using address information of the optical disk, and a distance to a target information track position is calculated. The linear motor is then controlled so that the head is moved by the calculated distance at high speed. In order to position the optical head at high speed and with high precision, the velocity or position of the linear motor is controlled using an external linear encoder or reflected diffraction light when light beams cross the tracks. At this time, if a signal from the linear encoder is inappropriate for any reason or if a focal point of the beam spot is not present on the disk surface and positional information of the linear motor cannot be obtained, the linear motor cannot be controlled and overruns. In this case, since the linear motor has only a finite operating distance, a head collides against a mechanical stopper and is stopped. Since the optical head is constituted by high-precision parts, if an excessive vibration or shock is applied thereto, the performance of the head is degraded, and in the worst case, the head is damaged and the apparatus malfunctions, resulting in a serious problem. In an information recording/reproduction mode, the linear motor is driven so that the beam spot is moved along information tracks. Therefore, the linear motor is driven in accordance with a tracking error signal or positional information from a tracking actuator. In this case, if a normal control state is disordered due to unexpected disturbance or the like, the linear motor overruns, and the same problem, as above, occurs.
The present invention has been made in consideration of the above situation, and has as its object to detect overrunning of a linear motor or a head to stop the linear motor, thereby preventing collision of the head against a stopper.
In order to achieve the above objects, there is provided an information recording/reproduction apparatus wherein a head performs information recording and/or retrieving and/or reproducing the recorded information on or from an information recording medium the head is moved relative to the recording medium and the head moving device is controlled properly according to the recording, reproduction time or the retrival time. The state of the head is monitored to determine if it falls within an appropriate range and a signal is limited to apply a damping force to the head when the head deviates from the appropriate range.
In this case, as to what kind of parameter or parameters is utilized to monitor the state of the head, there are various ways (e.g., as a parameter, to select a set of the position and the velocity of the head, or the velocity of the head alone, or the drive force of the head moving device), and the configuration of the appropriate range is determined according to each case, taking-several factors into account. In summary, any of them can be taken as long as the collision between the head and the stopper is certainly prevented, which is a final object.
First in order to achieve this final object, there is provided an information recording/reproduction apparatus for recording information on an information recording medium and/or retrieving and/or reproducing the recorded information therefrom, wherein a head is moved to perform the above operations relative to the recording medium. The position of the head on the recording medium is detected by a suitable detector and the velocity of the head is also detected. The actual head velocity is composed with a critical head velocity predetermined for each position on the recording medium. When the head velocity exceeds the critical velocity, a stop drive force is applied to the head.
According to a more detailed aspect of the present invention, the velocity of the head can be detected as follows. When the head moving device utilizes an electromagnetic effect due to a fixed magnetic field and a current flowing through a linear motor coil, as in a linear motor, the velocity of the head can be detected using a counter electromotive force generated in the linear motor coil.
Furthermore, in order to achieve the above object, there is provided an information recording/ reproduction apparatus for recording information on an information recording medium and/or reproducing the recorded information therefrom, wherein a head is moved in order to perform the above operations relative to the recording medium; a drive force of the head moving device is detected and it is determined whether or not the drive force of the head moving device falls within a predetermined level range. When the drive force of the head moving device exceeds the predetermined level range, a stop drive force is applied to the head moving means.